Nitric oxide synthase (NOS) is an enzyme which is found in humans. Three isoforms of NOS have been identified. In the body nNOS and eNOS are constitutively expressed in the cells in which they are found. However, iNOS is not constitutively expressed, but is known to be induced by a number of cytokines, lipopolysaccarides (LPS), and other mediators of the inflammatory response. Specifically, iNOS has been associated as indicating certain pathological disease states.
Alzheimer's disease (AD) is the major cause of dementia in the elderly. Although rare genetic forms of AD exist, most patients are classified as having sporadic AD, since no family history is usually identified. Pathologically, AD is characterized by neuronal and synaptic degeneration with an increased number of senile plaques and neurofibrillary tangles compared to non-demented individuals of comparable age.
The senile plaques, characteristic of Alzheimer's disease, are composed of a central core of aggregated beta-amyloid, a breakdown product of amyloid precursor protein (APP). The neurofibrillary tangles are insoluble intracellular thread-like structures made up of a hyperphosphorylated form of a protein called tau, which is associated with microtubles.
Early and accurate diagnosis of Alzheimer's disease is important since early intervention may delay or arrest the reversible neuronal damage. Clinical diagnosis is not always accurate since the criteria are relatively subjective and the disease needs to be differentiated from other dementing illnesses.